Television system



Patented July 16, 1946 r TELEVISION SYSTEM Cecil Oswald Browne, deceased, late of Buckinghamshire, by Margaret Winifred Browne, Gerrards Cross, and Ernest -William Tole, Bower Ashton, Long Ashton, England, administrators, and Henry William Hobbs, Haslemere, England, assignors to Electric & Musical Industries Limited, Hayes, England, a company of Great Britain Application March 7, 1944, Serial No. 525,408

In Great Britain March 17, 1938' This invention relates to television systems of transmission and reception in which a transmitting or a receiving station is mobile.

The invention is particularly, but not exclusively, concerned with aircraft television systems in which the television signals are transmitted from an airplane, for example, to a receiving station on the ground.

Assuming that a television picture of a portion of the ground beneath an aircraft is being transmitted therefrom and received by a ground station, in order that the received picture maybe more comprehensible to the operator of the receiver, it is essential that some indication should be given of the orientation of the received picture relatively to the points of the compass. When such indication is provided the received picture may be compared with a map of the district covered by the picture with greater facility.

In connection with aircraft television systems a picture may be transmitted having an indication on its surface such as the north point, this indication being controlled by a compass card associated with the transmitting equipment in the aircraft. The indication of the north point may 1 Claim. (Cl. 250-456) be obtained by projecting a white line or a small image of the compass card onto the picture resolving element of the transmitting camera. The

map associated with the receiver may then be orientated relatively to the received picture in accordance with the indication given,.or alternatively, the receiver itself may be adjusted relatively to the map, for example, by rotating the cathode ray beam deflecting means associated I with the receiving cathode ray tube. Again, the transmitting camera in an aircraft may be oriented by means controlled by a compass servomotor so that the scanned area always retains a definite relationship with the points of the compass.

The object of the present invention is to provide improved means for facilitating the correct orientation of the received images of transmitted subjects with respect to predetermined fixed points as, for example, the points of the compass.

According to the present invention in a method of operating a cathode ray tube provided with deflecting means, in order to produce a desired orientation of a subject to be transmitted or of a received image with respect to a' certain predetermined point or points, the scanning field set up by said deflecting means is adjustable angularly with respect to any fixed line inthe plane of the scanned area. In applying the invention to television systems, a scene or other subject transmitted to a receiver contains an indication of a fixed point such as the position of at least one of the points of the compass and at the receiver the deflecting means are adapted to adjust the scanning field so as to orientate the received image with the indication provided. p r In order that the invention may be more clearly understood and readily carried into efiect, cer: tain forms of deflecting apparatus embodying the invention will now be described in greater detail by way of example with reference to the accompanying drawings wherein: s Figure 1 shows a deflecting coil assembly for a vertically mounted receiving tube, p Figures 2 and 3 are detailed views of the brush mountings and slip rings, and

Figures 4 and 5 show modifications of the present invention. p Referring to Figure 1 of the drawings, a receiving cathode raytube 4 of which only a portion is shown has a deflecting coil assembly sup-- ported about its neck by a bracket 5 and platform 6, the bracket being suitably secured to the wall 1 of the receiver cabinet. For convenience in showing details, a portion of the coil assembly is shown in section and the other portion is an exterior view from a point degrees away from the point shown in section. A cylindrical mounting 8 contains a sleeve 9 carrying a coil l0 through which an adjustable direct current is passed in order to efiect adjustment of the nor-- mal or undeflected position of the electron beam in a known manner. The sleeve '9 is slidably adjustable within the mounting 8 in order to vary the position of coil l0 and may be clamped in a selected position by a screwed bolt II in a flanged collar I2. A drum shaped casing l3 is'provided with a worm-gear l4 which can be driven by a worm rod l5 operated by a flexible cable Hi from a wheel I! mounted outside the receiver cabinet and provided with a handle l8. W

A slip ring assembly is mounted above the drum I 3, being fixed thereto by pins 1 9. A flanged ring 20 of appropriate insulating material provides support for two further flanged rings 2| and 22 separated by a packing; ring 23. The'flan'ged rings of the packing ring are also made of insulating material. Each of the flanged rings 2| and 22. is formed with recesses to accommodate brass slip rings 24, 25, 26"and 21, the slip rings 25 and '26 lying in the recess formed by the flanged rings 2| and 22.. The slip rings are connected by leadsnot shown, to the deflecting coils 3 28 shown in dotted lines which are designed closely to embrace the neck of the tube 4 and fit tightly within the ring 20.

The slip ring assembly and brush mounting 29 are shown in greater detail in Figures 2 and 3 which are plan and side views respectively. The mounting 29 is supported from the ring l2 by a bar 33 of rigid insulating material whichis secured to the ring 9 by screws 3|. The section view of the brush mounting 29 shown in Figure 1 is taken on the line A\A in Figures? and 3. The brushes 32 are mounted in holders 33 and are held in contact with the slip rings by springs 34 and by the action of springs 35 tending to retate the brush holders about support posts 36. Conducting leads carrying the deflecting currents may be attached to the brush holders 33 by screw terminals or by soldering to the ends 31 of the brush springs 34.

It will be seen that the device described enables rotation cf the scanning coils to be effected in a convenient manner, rotation of the wheel I! being transmitted by the flexible driving cable Hi to the worm rod 15 and gear M which drives the casing I3 carrying the slip ring assembly and containing the deflecting coils 28. In operation the deflecting coils are rotated until the received picture is correctly orientated with respect to a compass point or other indication provided in the receiver by the transmitting camera. The adjustment may be continuous, for instance, when television signals are being received from a transmitting aircraft following an irregular or circular course.

Referring now to Figure 4, line and frame defleeting fields for a cathode ray tube in a television system are set up by asingle continuous wave wound coil it which replaces the separate sets of line and frame scanning coils usually employed. A number of equally spaced taps 39 in the coil are connected by leads 4|, of which four are shown, to segments 42 of a commutator switching device having as many segments as there are taps on the coil. Four brushes 43 arranged at 90 degrees to each other, serve to distribute to the segments 42 the line and field deflecting currents derived from appropriate defiection generators 4 and 41, respectively. Additional segments 49 interposed between the main segments ,2 and connected to them by resistances 5:] may be provided. Such additional segments serve to eliminate adverse effects due to unduly protracted interruption of the deflecting circuits.

It will be seen that in the operation of the arrangement shown in Figure 4, simultaneous rotation of the brushes 33 in a clockwise or counterclockwise direction will effect selection of a given set of tap points 39 to which the line and field deflecting currents are applied with consequent alteration in the orientation of the scanning field set up by the coils with respect to the points of the compass. In operation the rotation of the brushes 43 may be effected manually or automatically in accordance with compass indications.

In the alternative arrangement shown in Figure 5, separate sets of fixed line and field deflecting coils 5i and 52 are shown. A transformer 55 having a rotor and a stator carrying primary windings 53, 5'! and 58, 59 and secondary windings Si, 62 and 63, 66 respectively, is arranged so that the rotor carrying the primary windings may be rotated with respect to the stator. The line scanning coils 5! are connected to the secondary winding 6|, 52 while the field scanning coils 52 are connected to the secondary windings 53,

4 64, the primary windings 56, 51 and 5B, 59 being energized from the sources and 51 of line and field deflecting waveforms, respectively.

In operation of the arrangement shown in Figure 5, the scanning coils 5] and 52 are energized by the secondary windings to which they are connected, the magnitude of the voltages introduced in the secondary windings depending upon the relative angular displacement of the rotor primary windings to the secondary windings on the stator. The magnetic fields of the beam defleeting coils are thus rotated in sympathy with the rotor of the transformer, the movement of which is effected manually or automatically in accordance with compass indications.

In a further application of the invention, the orientation of a received picture may be made automatic by the use of a follow-up system including, for example, two photo-electric cells which are controlled by a compass indication. In such an arrangement the center of rotation of the compass indication lies on the axis of rotation of the scanning coils, and in order that the photo-electric cells may discriminate between the north point indication and other points of the compass, a portion of the transmitted picture coincident with the north indication is caused to be brighter than any similar area in the picture. At the receiver, the picture is observed by the two photo-electric cells which control, for example, a motor driving arrangement for the coils, the photo-electric cells being so mounted with respect to the received picture that as the bright area indicating the north point moves it becomes more efiective upon one cell than the other, thus causing the one cell and its associated circuit to energize the driving system and so to effect the necessary adjustment of the scanning coils.

In applying the invention to television systems employing a camera in which the average position of the scanning beam is substantially normal to the scanned area, as, for example, a camera having a transparent signal plate, in order that the picture may be transmitted with a definite orientation ascribed to the direction of the scanning lines, the position of the transmitting camera is fixed relatively to the aircraft and the scanning coils of the transmitting camera are rotated by mechanism controlled by a compass.

In any system embodying the invention, the transmitting camera may be fitted with aviewfinder which is preferably of the direct vision type, and a north point indication driven by the compass controlling the movement of the scanning coils is provided within the field of view transmitted by the camera. View finding may be aided by the use in the transmitting aircraft of a monitor tube situated close to the transmitting camera. The picture reproduced by the monitor tube would have the north point indication reproduced in it, thus facilitating continuous adjustment by the transmitter operator. Instead of a localized or a point indication, a. mesh of, for example, nine squares, orientated automatically by the compass servo-motor may be used. The squares of the mesh cooperating with corresponding fixed squares provided at the receiver enable positions of objects falling within the. field of View to be described with greater facility by the transmitter operator in the aircraft to the re-- ceiver operator on the ground.

Again, the invention may be applied to a system in which an image of a map or other surface is transmitted from an airplane, and in order to provide an indication of the direction in which;

the airplane is travelling with respect to the compas-s, points of the map, the transmitting scanning field is adjusted angularly with change in the course of the airplane by rotation of the scanning coils or adjustable selection of the tap points in a fixed coil as previously described in connection with Figure 4. The mechanism effecting the adjustment is operatively connected with the compass. Thus, the scanning field may be generated by a cathode ray tube of the receiver type and an image of the scanning field projected optically upon the surface of the map to be transmitted, a photo-electric cell being mounted adjacent the map and being energized by the light reflected from the map due to the scanning field, as in the method known as flying spot scanning.

Assuming for convenience of explanation that the airplane is flying due north and that the scanning lines are horizontally due east to west, then when the airplane changes course the scanning lines, owing to rotation of the scanning coils, will tilt in the direction of the new course. The received picture of the map will then be tilted with respect to the scanning lines of the receiving screen, thus giving an immediate indication of the change of course of the airplane.

While reference in detail has been made only to electro-magnetic scanning arrangements, it will be understood that theinvention may be applied to electrostatic scanning arrangements. Thus, for example, though the deflecting plates in the electrostatic case are usually mounted within the tube, they may be mounted externally and means for rotating them may be provided.

Having now described our invention, What we claim as new and desire to have protected by Letters Patent is:

A deflecting yoke for a cathode ray tube wherein a cathode ray beam is adapted to be produced, comprising a continuous tapped electromagnetic winding for producing deflecting fields in response to the application of deflecting potentials to certain of the taps of the winding, and switching means for selecting different taps of the winding in order to alter the direction of deflection of the cathode ray beam.

MARAGARET WINIF'RED BROWNE, ERNEST WILLIAM TOLE, Joint Administrators for Cedil O. Browne,

(Deceased).

HENRY WILLIAM HOBBS. 

